Solution pH: A Selectivity Switch in Aqueous Organometallic Catalysis—Hydrogenation of Unsaturated Aldehydes Catalyzed by Sulfonatophenylphosphane–Ru Complexes

The equilibribrium distribution of water-soluble ruthenium hydrides [HRuCl(tppms)₃] and [H₂Ru(tppms)₄] (tppms = (3-sulfonatophenyl)diphenylphosphane) in the reaction with H₂ is governed by the pH value. As a consequence, the selectivity in the hydrogenation of cinnamaldehyde for reaction at C=C or C=O can be completely inverted by changing the pH value (see drawing below).     

Transfer Hydrogenation of Ketones Catalyzed by 1-Alkylbenzimidazole Ruthenium(II) Complexes

Summary. Six [RuCl₂(1-alkylbenzimidazole)(p-cymene)] complexes have been prepared and the new compounds characterized by C, H, N analyses, ¹H NMR, and ¹³C NMR. The reduction of ketones to alcohols via transfer hydrogenation was achieved with catalytic amounts of the complexes in the presence of t-BuOK.     

Ruthenium(II)-salen complexes-catalyzed olefination of aldehydes with ethyl diazoacetate

Several salen-ruthenium(II) complexes, which are derived from commercial ligands or simply ethylenediamine, can be successfully applied as catalysts for the olefination of a broad variety of aldehydes. Depending on the electron richness of the applied aldehydes, good to very good olefin yields and high E:Z selectivities are reached at 60 or 80 °C reaction temperature with ethyl diazo acetate being the reaction partner. The reaction rate depends on the electron donor capabilities of the aldehydes. Electron poor aldehydes undergo faster reactions than electron rich aldehydes, but both electron rich and bulky aldehydes can be transformed to corresponding olefins in very good yields and high E-selectivity.     

Highly Efficient Conversion of Homocoupling and Heterocoupling of Terminal Alkynes Catalyzed by AuCu24/AC-200

Regulation of Hybrid Materials of Ministry of Education, Bimetallic nanoclusters with synergistic effect exhibit better stability and activity than monometallic nanoclusters in catalytic applications. However, the large number of ligands on the surface of nanoclusters obscure the active sites, thus reducing the catalytic activity. Here, AuCu₂₄/AC−X (X=0, 200, 300, 500, 800) catalysts were fabricated by removing the partial ligands on the surface of AuCu₂₄H₂₂((p-FPh)₃P)₁₂ nanoclusters (short for AuCu₂₄ NCs), and investigated the influence of calcination temperature on catalytic performance of AuCu₂₄/AC in homocoupling and heterocoupling of terminal alkynes. The results showed that the catalytic activity of AuCu₂₄/AC−X exhibited a volcanic trend with the increase of X (heat treatment temperature) and the content of Cu²⁺ also changed with the increase of X. Compared with Au₂₅/AC-200 and Cu₂₅/AC-200 catalysts, the AuCu₂₄/AC-200 bimetallic catalyst showed the highest catalytic activity in homocoupling and heterocoupling of terminal alkynes under mild conditions with TOF values reaching 478.7 h⁻¹ and 114.1 h⁻¹ respectively, which are higher than most reported catalysts. This work provides a research idea for the design of bimetallic nanoclusters with superior performance.     

Cationic Gold(I) Complexes: Highly Efficient Catalysts for the Addition of Alcohols to Alkynes

Gold complexes are almost unknown in homogeneous catalysis , and for a long time gold was even thought of as “catalytically dead”. This is clearly not the case for cationic phosphanegold(I ) complexes (see reaction below), which can catalyze the addition of alcohols to alkynes with turnover frequencies up to 1.5 s⁻¹ and total turnover numbers up to 10⁵! R=H, alkyl, Ph, CH₂OH.     

Benzonitrile Hydrolysis Catalyzed by a Ruthenium(II) Complex

The rate constant for the basic hydrolysis of benzonitrile (PhCN) to benzamide (PhCONH₂) in the [Ru^II(tpy)(bpy)] moiety (tpy = 2,2' : 6',2"-terpyridine, bpy = 2,2'-bipyridine) (k_OH = 3.7 2 10^-2 M^-1s^-1) is 5 2 10³ times higher than that of the free ligand and two times higher than that corresponding to the analogous acetonitrile complex. This effect is unusual for a transition metal in the (II) oxidation state, and can be attributed to the π-electron acceptor properties of both the polypyridyl ligands and the phenyl group. Since amides, being poor π-acceptor ligands, are rapidly released from the coordination sphere of ruthenium(II), the final product of this process is the [Ru(tpy)(bpy)(OH)]⁺ complex. The activation parameters for this nitrile hydrolysis have been determined and compare reasonably well with other values for similar reactions.     

Intermolecular Methoxycarbonylation of Terminal Alkynes Catalyzed by Palladium(II) Bis(oxazoline) Complexes

Boxing clever : Direct conversion of a terminal alkyne group into a β‐methoxyacrylate is realized with the aid of the bis(oxazoline) ligand (box). Acetyl and ketal protecting groups, free hydroxy groups, and acid‐sensitive glycosidic bonds are not affected under the reaction conditions. The one‐pot synthesis of (±)‐dihydrokawain from the homopropargyl alcohol is also achieved. tfa=trifluoroacetate

     

Nickel‐Catalyzed Reductive Coupling of Aldehydes with Alkynes Mediated by Alcohol†

A nickel‐catalyzed reductive coupling of aldehydes with alkynes using 1‐phenylethanol as reducing agent has been developed. The key achievement of this work is that we demonstrate environmentally benign 1‐phenylethanol can serve as a viable alternative reducing agent to Et₃B, ZnEt₂ and R₃SiH for the nickel‐catalyzed reductive coupling reaction of aldehyde and alkynes.     

Anti-Markovnikov Addition of Anilines to Aliphatic Terminal Alkynes Catalyzed by an 8-Quinolinolato Rhodium Complex

Anti-Markovnikov addition of anilines to aliphatic terminal alkynes proceeded using an 8-quinolinolato rhodium/phosphine catalyst system. The use of a strong organic base, 1,1,3,3,–tetramethylguanidine, in the catalyst system enabled the formation of the aldimine products. Substrates with various functional groups including polar groups such as a phenolic hydroxy group are applicable to the hydroamination.     

水溶性salen-Co（III）配合物催化的端炔水合反应

报道了一种用于端炔水合反应的水溶性salen-Co(III)配合物催化剂,在使用硫酸作为共催化剂的条件下能高效得到产物甲基酮。该催化剂用量少,反应结束后可利用简单的萃取实现产物与催化剂分离,简化了后处理过程。此外,催化剂还可回收重复使用,但催化剂活性会略有下降。     

取代联吡啶钌配合物对末端炔烃的催化环三聚作用

RuCl3·3H2O分别与6,6’-二甲基-2,2’-联吡啶(dmbp)和2,2’-联吡啶-6,6’-二甲醛(bpda)反应生成[cisRu(L)2Cl2]Cl·2H2O(L=dmbp,bpda),进一步用CF3SO3Ag脱氯得到[cis-Ru(L)2(H2O)2](CF3SO3)3.研究了4种配合物对1-己炔、苯乙炔和丙炔酸乙酯的催化环三聚作用,发现脱氯后的含水配合物催化活性有显著提高;体系中有水存在时,丙炔酸乙酯环三聚具有很强的区域选择性.催化机理研究表明,该催化过程为催化[2+2+2]环加成反应.钌杂环庚三烯或7-钌杂双环[2.2.1]-2,5-庚二烯是关键中间体,联吡啶配体上的6-甲酰基取代基水合后通过与丙炔酸乙酯的羰基形成分子内氢键影响环三聚产物的区域选择性.     

A new protocol for synthesis of bifunctional alkynyl[vinyl or (E)-alkenyl]substituted organosilicon compounds

A new efficient route for selective synthesis of various, novel alkynyl(vinyl)substituted silicon (6) and alkynyl[(E)-alkenyl]substituted silicon compounds (9) via silylative coupling of alkynes and their products catalyzed by ruthenium(+2) complexes is described. The tandem procedure facilitates the formation of 9 synthesized in a high yield and stereoselectivity by a sequential silylative coupling of terminal alkynes with divinylsubstituted silicon compounds followed by silylative coupling reaction of 6 with styrenes in the presence of ruthenium hydride complexes ([RuHCl(CO)(PR₃)_3−n]; R = Cy (n = 1), i-Pr (n = 1), Ph (n = 0)).     

Zinc‐Catalyzed Dehydrogenative Cross‐Coupling of Terminal Alkynes with Aldehydes: Access to Ynones

Because of the lack of redox ability, zinc has seldom been used as a catalyst in dehydrogenative cross‐coupling reactions. Herein, a novel zinc‐catalyzed dehydrogenative C(sp²)? H/C(sp)? H cross‐coupling of terminal alkynes with aldehydes was developed, and provides a simple way to access ynones from readily available materials under mild reaction conditions. Good reaction selectivity can be achieved with a 1:1 ratio of terminal alkyne and aldehyde. Various terminal alkynes and aldehydes are suitable in this transformation.     

Highly Active Ruthenium Catalysts for Olefin Metathesis: The Synergy of N-Heterocyclic Carbenes and Coordinatively Labile Ligands

Two N-heterocyclic carbene ligands at once may be one too many , at least if you intend to have highly active ruthenium catalysts for olefin metathesis. Density functional calculations recommend the replacement of the second carbene ligand in the successful ROMP catalysts 1 by coordinatively more labile ligands as in 2 or 3 . In both cases, the catalytic activity is greatly improved.     

Minimizing Side Product Formation in Alkyne Functionalization of Ruthenium Complexes by Introduction of Protecting Groups

The synthesis of alkyne functionalized bipyridine ruthenium complexes are reported. The improved synthetic approach through application of stable protecting groups prevents formation of possible side products while facilitating purification. By applying copper-catalysed azide-alkyne cycloaddition reactions (CuAAC) pyrene units with flexible alkyl linkers are introduced at the periphery of the complex, opening up various applications including surface immobilization and DNA intercalation. All complexes are characterized structurally as well as photophysically, especially regarding the influence of the introduced alkyne and triazolyl substituents on their photophysical behavior.     

Ruthenium(II)-catalyzed para-selective CH difluoroalkylation of aromatic aldehydes and ketones using transient directing groups

A Ru(II)-catalyzed para-difluoroalkylation of aromatic aldehydes and ketones with a transient directing group has been developed. It utilizes less expensive ruthenium catalysts and allows facile access to challenging difluoroalkylated aldehydes. The mechanism studies suggest that the distinct coordination mode of ruthenium complex with imine moieties is responsible for para-selectivity.